Control device



July 8, 1941.

. I. HOLMES CONTROL DEVICE Filed Jan. 12, 1939 IIIII;

I I I I I I I I I I I I I I I I I I I I I I Fi .s

Gifford. I. Holmes 'Clitorngg Patented July 8, 1941 CONTROL DEVICE Gifford I. Hohnes, Minneapolis, Minn., assignor to Minneapolis-HoneywellRegulator Company, Minneapolis, Minn., a corporation of Delaware Application January 12, 1939, serial No. 250,537

(Cl. aol- 55) Claims.

This invention relates to a control device, and more particularly to that type of controller which is utilized in proportioning electrical control circuits.

A broad object of this invention is to provide a control device which is of simple sturdy structure, positive in operation, and possessing a high degree of sensitivity. A further object is to minimize the inaccuracies in devices of this type, due to the high coefficients of friction of resistance materials, by substantially reducing the contact area between the moving elements of the device.

A still further object of the present invention is to provide a tapered resistance effect as electrical resistance is placed into or out of circuit between extremities of the resistance element.

Another object is .to obviate tap resistances with commutators, commutator lead wires, and

- the like, all of which tend to add numerous parts to the device with a concurrent rise in cost of production as well as the greater probability of failure of a part due to faulty assembly.

Further objects will be apparent by study of the following specification, the appended claims, and the drawing, of whichr Fig.l is an elevation of a preferred embodiment of my invention with the cover removed;

Fig. 2 is a sectional view with parts in elevation taken along the line 2-2 of Fig. 1;

Figs. 3 and 4 are diagrammatical views of modifications; and

Figure 5 is a detail view of the resistances.

Referring more particularly to the drawing, in Figures 1 and 2 a preferred form of my invention is shown. The device comprises a base- I8 which has inturned ears II to provide for suitably mounting the device by means of the screws I2. Holes I3 are provided in the base I8 and register with the inturned ears II so that the screws I2 maybe readily inserted into the Wall. 1p-

A protective cover I4 is secured to the base I8 by means of an indentation I4a which ts into a hole I8d in the top of the base I8 and a slot I4b which cooperates with a thumb screw I8b in the bottom of the base I8. The ,cover I4 is provided with elongated slots I4c at both top and bottom to allow free circulation of air through the interior'thereof. Slot I4d is provided in the top of the cover I4 through which the adjustment knob 28 protrudes. An upturned fixed pointer 28d is provided adjacent the slot Ild and is adapted to cooperate with an adjustment knob 28 to register the manual temperature setting.

Carried on the base I8 and conventionally secured thereto is an insulating panel I5 upon which is mounted a thermostatic element I6. The thermostatic element I6 is riveted to a bracket Il which is in turn secured to a rotatably mounted post I8 which is carried by the insulating panel l5. Also secured to the base I8 is the adjustment knob 28 mounted upon a post 2I. The adjustment knob 28 carries an adjustment cam 22 which is adapted to cooperate with an adjustment cam follower lever 23 to position the bimetallic element I8 through the rotatable post I8. Spring 35 is suitably secured between an inturned ear 36 on the adjustment lever 23 and a bracket 3l and thereby maintains the adjustment lever 23 in engagement with the adjusting cam 22. A

Also carried on the insulating panel I5 is a smaller panel 25 to which are secured clips 26 into which a resistance element 2l is adapted to fit. A second resistance element 28 is carried at the extremity of a slider bar 29 which is actuated by the bimetallic element I6 in a manner that results in a rotating movement of the resistance element 28 about the post I8. The resistance element 2l is disposed in relation to the resistance element 28 in a plane parallel to the plane in which the resistance element 28 rotates about its center of rotation at I8. Being in parallel planes,

` therefore, the resistance to sliding movement between the resistance elements 2l and 28 will be` only the sliding friction of the contact area. between the two resistances, which is a very small area as will be hereinafter set forth.

The slider bar 29 is provided with an enlarged internally threaded adjustment portion 29a at its lower extremity which cooperates with a threaded stem 38 upon the bracket 3I carried by the bimetallic element I6 to provide for a manual adjustment of the resistance element 28 in respect to the resistance element 2l. A lock nut 32 is also provided upon the threaded stem 38 to secure the slider bar 29 in its adjusted position.

The resistance element 2l is provided with electrical leads 44 and 45 at its extremities. The resistance element 28 is electrically connected to the slider bar 29 which is of electrically conductant material. Therefore the current is conducted from the resistance 28 through the slider bar 29 through the stem 38, the bracket 3l, the bimetal I6, bracket I1, post I8 to"Y the electrical lead wire 46. Therefore, it is seen that three electrical connections are provided in a conventional manner for devices oi this general type.

To manually set the device to operate at a desired temperature, the adjustment knob 28 and the cam 22 secured thereto are rotated. Rotation of the knob 28 is limited by a stop 48 which cooperates with an arcuate slot 4I in the cam adjusting knob 28 to limit rotation in either clockwise or counter-clockwise direction. When the adjustment cam 22 is moved in a clockwise direction the 'cam follower lever 23 will be moved to the right. Upon movement to the right by the cam follower lever 35, the pin I8 upon which the bimetallic element I6 is mounted will be rotated in a clockwise direction. Therefore, the resistance element 28 will be moved towards the right end of the resistance element 21 and the operating temperature of the device will be changed.

The device shown in Figures l and 2 is adapted to insert a greater amount of resistance into a circuit for a given movement of the sliding resistance 28 across the resistance 21 than could be obtained by a conventional straight resistance and a slider bar cooperating therewith. This is accomplished by providing the resistance element 28 in cooperative relation with the resistance element 21 which is arcuate in shape. Therefore, as the resistance 28 moves from the mid position shown to either extremity of the resistance 21,

y the amount ofv resistance between the mid portion of the resistance 21 to its extremity will be brought into, the circuit, as well as the amount of resistance of the resistance element 28 that will be brought into the circuit between its contact point when in mid position and its contact point when at `the extremity of the resistance 21. This point of contact at the extremity of resistance 21 will be nearer the upper extremity of the resistance 28 than when the resistance is in the mid position. The resistance then in the circuit will be the resistance of the resistance element 21 from mid position to its extremity plus the nesistance of resistance element 28 brought into circuit by the action of the slider bar 28 moving about a substantially greater radius of rotation than the curvature f the resistance element 21. Therefore, the cooperation of the two resistance elements 21 and 28 will result in a tapered eiect in the resistance brought into the electrical circuit inasmuch as a greater amount of resistance is brought into circuit for a given movement of the sliding resistance 28 across the resistance 21 than could be obtained by moving a slider bar across a straight resistance.

Referring now to Figure 5, the two resistance elem-ents 28 and 29 are shown in greatly enlarged detail. The resistance wire of the element 28 is coiled about an insulating core 58 which is suitably secured to the slider bar28 (not shown). It will be noted that the convolutions of the resistance wire are held in spaced relationship to each other. Such arrangement prevents short circuiting between the convolutions. The resistance wire of the element 21 is likewise coiled about an insulating core The convolutions are also spaced to prevent short circuiting. The core 5I which carries the insulating wire 21 may be of a material which can be moulded so that the curvature of the resistance element 21 may have electrical characteristics which are suitable to the application of the device.

It will be noted that the contact area between the resistance 28 and the resistance 21 'is substantially reduced because of the double curva,- ture of the elements. The helical ceiling of the resistance material, as well as the circular crosssectional conguration of the wire, will, when the two elements are brought into engagement, cause them to present a very small contact surface to each other. Because of the small contacting area between the surfaces o f double curvature, resistance elements of the chrome-nickel variety, which have very high surface resistance, can be used. Another feature of reducing the surface contact is that the frictional resistance to sliding between the members is reduced and hence the device can be more sensitive, as-the tendency' to have a jumpy action will be likewise reduced.

That form of my invention which is diagrammaticaliy shown in Figure 3 comprises a bimetallic element IIB which is secured to a bracket II1 which is in turn secured to a mounting post I I8. The bimetallic element I I8 carries a bracket I 3I- which carries a slider bar |28 provided with an adjustment I28a and a lock nut |82 similar to that shown in Figures l and 2. The resistance element |21 has a radius of curvature that is smaller than the radius of rotation of the elementl28 and is adapted to cooperate with the curved resistance element |28 in a. manner to cut out resistance from the element I 28 as the slider bar |28 moves from the mid position shown to an extremity of the resistance element I21 inasmuch as the center of curvature of the eiement I21 lies between the point of contact of the two elements and the center of rotation III of the element |28.4

.wire carried upon a slider bar In Figure 4, a modiiication of my invention is shown which employs a conventional straight resistance element 221 comprising several turns of coiled resistance wire. The contactmember 228 is comprised of several turns of conductive 228 which is rotated.by a bimetaliic element 2I8 in a manner similar to that pointed out in connection with Figures 1, 2, and 3. An advantage of the device shown in Figure 4 is that the contact friction and the corresponding resistance to sliding is substantially reduced because of the small contact area between the surfaces of double curvature of the resistance element 221 and the contact element 228.

Many modifications and forms of this invention will occur to those skilled in the art, therefore it should be clearly understood that I am not to be limited only to those forms shown and described but by the scope of the appended claims.

I claim as my invention:

1. An adjustable electrical resistance comprising, in combination, a pair of resistance elements in slidable electrical contact with each other,

resistances with reexternal circuit,

2. Anadjustable electrical resistance comprising, in combination, a pair of elongated resisty ance elements abutting each other at a point of contact, said elements being at substantially a. degree angie to each other at Said point oi' contact, and means for slidingl said resistances with respect to each other to vary said angle whereby said point of contact moves longitudinally with respect to both of said resistance elements. f

3. In a control device, in combination, a condition responsive element ilxed at one end and having a free end which is movable in accordance with variations in a variable condition, an arm having one end secured to said free end of said element and moved thereby upon changes in said condition, a ilrst resistor, said resistor being ately formed resistor, the axis of which lies in a plane that is substantially parallel to the plane of the travelled arc of movement of said ilrst resistor, said second resistor being arranged so that said two resistors will be in slidable engagement for the entire movement of said first resistor through its arcuate course of travel, said center of said arc of travel of said irst resistor and the arc of curvature of said second resistor being so selected that the point or points of contact of both said resistors will be varied by the movement of said rlrst. resistor through its travelled arc.

5. In a control device, in combination, a condition responsive element adjustably ilxed at one end and having a free end which is movable in accordance with variations in a variable condition, an arm having oneV end secured to said free end of said element and moved thereby upon changes in said condition, a iirst resistor, said resistor being mounted upon the free end of said arm and moved thereby in an arc. a second arcuately formed resistor, the axis of which lies in a plane that is substantially parallel to the plane of the travelled arc of movement of said ilrst resistor, said second resistor being arranged so that said two resistors will be in slidable engagement for the entire movement orsaid nrst resistor through its arcuate course of travel, said center of said arc'of travel o! said first resistor and the arc of curvature of said second resistor being so selected that the point or points of contact of both said resistors will be varied by the movement of said first resistor through its travelled arc, an elongated adjustment arm secured to said adjustably iixed end o! said condition element, saidadjustment arm being capable of varying the position of said iixed end to'change the setting of said element, a cam for moving said adjustment arm, spring means for biasing said arm into engagement with said cam, and manual setting means for changing the position 'of said cam to thereby vary the position of said adjustment arm.

6. In a control device, in combination, a first resistance element comprising a length of electrical resistance wire helically wound into a series of convolutions upon an insulating longitudinal core. said convolutions being held in spaced relationship to each other to inhibit short circuitingtherebetween, a second resistance element comprising a length of resistance wire helically wound into a series of convolutions upon an insulating longitudinal core, said convolutions likewise being held in spaced relationship to each other to inhibit short circuiting therebetween, a thermostat having one end xed and the other end movable in accordance with variations in temperature, and a slider arm for mounting said second resistance element carried by the free end oi' said thermostat. said slider arm maintaining said second resistance element in slidable engagement with said iirst resistance element so that the contact point or points for both of said resistances may be varied in accordance with variations in temperature which affect said thermostat.

7. In a control device, in combination, a rst resistance element comprising a length of electrical resistance wire helically wound into a series of convolutions upon an insulating longitudinal core, said convolutions being held in spaced relationship to each other to inhibit short circuiting therebetween, said core being formed into an arc of which the axis lies in a nrst plane, a second resistance element comprising a length o! resistance wire helically woundinto a series of convolutions upon an insulating longitudinal core, said convolutions likewise beingv held in spaced relationship to each other to inhibit short circuiting therebetween, the axis of said second resistance element being arranged in a plane which is substantially parallel to said rst plane, a thermostat having one end fixed and the other t end movable in accordanceA with variations in temperature, a slider arm for mounting said second resistance element carried by `the -free end of said thermostat, said slider arm maintaining. said second resistance element in slidable engagement with said first resistance element so that the contact point or points for both or vsaid resistances may be varied in accordance with variations in temperature which aiect said thermostat, and an adjustment associated with said slider arm for varying the control point of the device.

8. An adjustable electrical resistance comprising, in combination, a pair of resistance elements in slidable electrical contact with each other, condition responsive means movable in accordance with variations in a variable condition, and means moved by said condition responsive means for sliding said resistances with respect to each other for progressively varying the resistance included in an external circuit of each of said resistance elements. Q

9. An adjustable electrical resistance comprising, in combination, a relatively fixed iirst resistance element, a relatively movable second resistance element in slidable electrical contact with said ilrst resistance` element, condition responsive means movable in accordance with variations in a variable condition, and means moved by said condition responsive means for sliding said second resistance element with respect to said first resistance element for progressively varying the resistance included in an external circuit of each of said resistance elements.

10. An adjustable electrical resistance comresistance element abutting said first resistance element at a point of contact, said elements being at substantially a degree angle to each other at said point of contact, condition responsive means movable in accordance with variations in a variable condition, and means moved by said condition responsive means for sliding said second resistance element with respect to said ilrst resistance element to vary said angle whereby said point of contact moves longitudinally with respect to both oi' said resistance elements.

GIFFORD I. HOLMES. 

